Polymerization of methyl methacrylate with a thermal iniferter: Diethyl 2,3‐dicyano‐2,3‐di(p‐tolyl)succinate

A hexa‐substituted ethane type compound, diethyl‐2,3‐dicyano‐2,3‐di(p‐tolyl)succinate (DCDTS), was successfully synthesized and used for initiation of methyl methacrylate (MMA) polymerization. The reaction demonstrated the characteristics of a “living” polymerization; i.e., both the yield and the molecular weight of the resulting polymers increased linearly with increasing reaction time, the molecular‐weight distribution of PMMA obtained was ～1.60 and almost unaffected by the conversion, and the resultant polymer can be chain extended by adding fresh MMA. End group analysis of the resultant PMMA confirmed that DCDTS behaves as a thermal iniferter for MMA polymerization. A block copolymer was prepared from the resultant PMMA, which contains a hexa‐substituted C? C bond functional end group. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2566–2572, 2001     

Self‐assembled centimetre‐sized rods obtained in the oxidation of o‐phenylenediamine and aniline

Morphologically well‐defined rods of approximately 1 cm in length are effectively and economically obtained by mixing ortho‐phenylenediamine (30 mmol L^?1) with ammonium persulfate (12.5 mmol L^?1) in an acidic solution (0.37 mol L^?1 HCl) at room temperature with and without the presence of 50 mmol L^?1 aniline. These self‐assembled, morphologically uniform products can be potentially scaled up and used as morphological templates to fabricate well‐defined structures of other materials such as conducting polymers. The products were characterized using Raman, UV‐visible, high‐resolution NMR (¹H and ¹³C) and mass spectroscopies, X‐ray diffraction, scanning electron microscopy and elemental analysis. Apart from certain differences in visual appearance and in X‐ray diffractograms, other analytical data suggest that there are no structural changes upon addition of aniline into the reaction mixture. NMR and mass spectra imply that all syntheses carried out either with or without aniline result in a mixture of two products, attributed to 2,3‐phenazinediamine and 3‐aminophenazin‐2‐ol. A formation mechanism based on hydrogen bonding and π–π stacking has been proposed. © 2015 Society of Chemical Industry     

Preliminary Investigation of Manganese-Catalyzed Ozonation for the Destruction of Atrazine

A preliminary experimental study conducted with a conventional bubble ozonation contactor column has shown that small amounts of Mn(II) greatly enhanced the destruction of atrazine by ozone. There is an inversely linear relationship between the dosed Mn(II) concentration and the residual ozone concentration at a specific reaction time. The ozone transfer efficiency into water is greater with the increase of Mn(II) dosage. Hydrous manganese dioxide prepared by reacting permanganate with manganese sulfate, also was shown to be effective in catalyzing the destruction of atrazine by ozone. The efficiency of catalytic activity for the destruction of atrazine caused by preformed hydrous Mn(IV) is slightly lower than the case of Mn(II). A lower residual ozone value using manganese dioxide compared to the case of ozone alone suggests that ozone also may be decomposed by hydrous Mn(IV). However, a commercial MnO₂ did not show any catalytic activity for atrazine destruction. The very much greater degree of atrazine oxidation by manganese-catalyzed ozonation compared to ozone alone is speculated to be the result of the generation of highly oxidative intermediate species such as hydroxyl radicals during the reaction between ozone and manganese species.     

Promotion in Heterogeneous Catalysis: A Topic Requiring a New Approach?

Promoters, and their counterparts poisons, are two topics that have been studied extensively since heterogeneous catalysts have been used industrially. Commercial catalysts tend to involve multiple promoters to enhance the activity, selectivity, lifetime and structural integrity, in addition to guard beds or feedstock purification measures that are used to avoid the adsorption of poisons. Yet, at a fundamental level, there is still considerable debate as to how specific promoters function. Promoter effects tend to be specific to a particular catalyst formulation and generic effects are not common, yet this would be desirable. Generally, in acid catalysis and hydrogenation reactions, promoter effects can be dramatic and unexpected. However, in oxidation reactions of alkanes and alkenes, the promotion effects observed to date are somewhat limited. In this paper, the topic of promotion in heterogeneous catalysis is discussed. The complex interplay between structural and electronic effects of promoters is described using examples of both well defined metal surfaces (e.g., the promoted iron catalyst for ammonia synthesis) and multicrystalline metal, metal oxide and metal phosphate catalysts (e.g., Li-doped MgO for methane oxidation). Subsequently, a molecular approach for the promotion of heterogeneous catalysts is prepared and discussed. This is based on observations from well defined molecular catalysts for homogeneously catalysed processes of ligand accelerated reactions. Examples are described where the effects of ligand acceleration, increasing reaction rate by over two orders of magnitude, can be observed for heterogeneous catalysts for hydrogenation and acid catalysed reactions. The remaining challenge is to identify similar effects for partial oxidation reactions, and it is questioned whether a molecular approach can be developed to meet this challenge.     

Structure–Activity Relationships of Benzenesulfonamide‐Based Inhibitors towards Carbonic Anhydrase Isoform Specificity

Carbonic anhydrases (CAs) are implicated in a wide range of diseases, including the upregulation of isoforms CA IX and XII in many aggressive cancers. However, effective inhibition of disease‐implicated CAs should minimally affect the ubiquitously expressed isoforms, including CA I and II, to improve directed distribution of the inhibitors to the cancer‐associated isoforms and reduce side effects. Four benzenesulfonamide‐based inhibitors were synthesized by using the tail approach and displayed nanomolar affinities for several CA isoforms. The crystal structures of the inhibitors bound to a CA IX mimic and CA II are presented. Further in silico modeling was performed with the inhibitors docked into CA I and XII to identify residues that contributed to or hindered their binding interactions. These structural studies demonstrated that active‐site residues lining the hydrophobic pocket, especially positions 92 and 131, dictate the positional binding and affinity of inhibitors, whereas the tail groups modulate CA isoform specificity. Geometry optimizations were performed on each ligand in the crystal structures and showed that the energetic penalties of the inhibitor conformations were negligible compared to the gains from active‐site interactions. These studies further our understanding of obtaining isoform specificity when designing small molecule CA inhibitors.     

Electrically insulating polymeric nanocomposites with enhanced thermal conductivity by visible‐light curing of epoxy–boron nitride nanotube formulations

Epoxy–boron nitride nanotube (BNNT) composites were prepared using visible light through a radical‐induced cationic polymerization method activated by camphorquinone. The fully cured films showed an enhancement of glass transition temperature in the presence of the filler. Electrical characterization showed a slight dielectric constant decrease with BNNT content. Finally, thermal conductivity measured using nano‐flash analysis showed a linear increase in the thermal conductivity of the materials with increasing BNNT content in the photocurable formulations. © 2017 Society of Chemical Industry     

Effect of thermal conditioning on the initiation threshold of secondary high-explosives

While most performance metrics of high-explosive (HE) based devices like detonation velocity, detonation pressure, and energy output are expected to degrade over time, the evolution of initiation threshold appears less clear, with claims of both increasing and decreasing trends in threshold having been made in the literature. This work analyzes D-optimally designed sequential binary test data for a few thermally conditioned porous-powder and polymer-bonded HE initiator systems using a Bayesian likelihood method employing the probit regression model. We find that in most cases the initiation threshold decreases (i. e., sensitivity increases) upon accelerated thermal conditioning. However, such results are nuanced and influenced by factors like the contact area of initiating stimulus, HE characteristics like density and specific surface area, as well as possible thermally induced changes to other materials and interfaces involved.     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

The electrochemical reduction of VO2 in acidic solution at high overpotentials

An investigation has been carried out to attempt to understand the unusually low apparent symmetry factor observed during the reduction of V(5) at higher overpotentials at carbon electrodes (typically <0.13, or >460 mV decade⁻¹). This reaction is of interest because it occurs in vanadium redox-flow batteries (VRBs) during discharge. Polarisation curves were measured using a rotating disk electrode (RDE). The reaction was not solution mass transport controlled, was pH independent (ca from 0 to 1), and the observed Tafel slope was unaffected by V(5) concentration over a range from 0.031 to 280 mM. Electrode double layer capacitance measurements were also carried out in sulphuric acid with and without vanadium. These tests showed that the presence of V(5) caused a suppression of the normal carbon surface quinone pseudocapacitance, as well as the appearance of two new pseudocapacitance peaks, one around 0.175-0.2 V and the other around 0.675-0.725 V versus SCE. The observed results do not appear consistent with a precipitated film causing diffusion limitations or causing IR drop. A model is developed to try to explain the data, which involves electron transfer through an adsorbed layer of vanadium.